BLASTING GELATINE, BALLISTITE AND
PROGRESSIVE-POWDER

purposes, and was too liable to undergo changes while stored. It
would seem, however, that the experiments helped in their way
towards the achievement of Nobel's next important discovery,
namely ballistite, or almost smokeless nitro-glycerine powder.

In that interesting and well-written paper previously referred to,
which Alfred Nobel read before the Society of Arts in London on
the 2ist May, 1875, he describes the properties required in an
explosive suited for practical use, and the advantages and defects
of the black powder which had been used through the centuries,
in the following way :

" It is not sufficient, indeed, that a substance is explosive, or
even powerfully explosive, to render it useful for practical purposes.
There are a great many other questions which have to be con-
sidered ; in the first instance, whether it compares favourably with
those substances already in use which it has to compete with ;
again, if the same power can be lodged in the same bulk; what
the cost of manufacture is, and what danger or difficulties attend
it; whether it offers the necessary chemical stability in all climates ;
whether its carriage and use are not too dangerous for its practical
utilisation; whether it is hygroscopic, and how it is affected by
contact with water; and finally, what influence the gases or fumes
produced by the explosion may have on the health of the miners*

" This explains why it is difficult, even with more powerful
explosives at command, to supersede gunpowder. That old mix-
ture possesses a truly admirable elasticity which permits its
adaptation to purposes of the most varied nature. Thus, in a
mine, it is wanted to blast without propelling ; in a gun to propel
without blasting; in a shell it serves both purposes combined; in
a fuse, as in fireworks, it burns quite slowly without exploding.
Its pressure, exercised in those numerous operations, varies between
one ounce (more or less) to the square inch, in a fuse, and 85,000 Ite,

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